IO-360 A1A What Mag Timing 20 or 25 Deg. BTDC?

[garytex]

 

I noticed that Jetdriven mentioned that he had his timing changed from 20 deg. BTDC to 25 deg. with better performance noted, especially LOP.  The below info from the type certificate for the I0-360 A1A ends with the note that 25 deg. is spec, with 20 deg optional.  Pretty weird, huh?  So, how is your timing set, why, and what effect do you see?  Anyone else changed timing and has before and after?

 

 

 

 

 

 

 

1E10 Page 2 of 18 

Model    (cont'd) IO-360-A1A, -A1B, -A1B6, -A1B6D, -A1C, 

            -A1D, -A1D6, -A1D6D, -A2A, 

            -A2B, -A2C, -A3B6,-A3B6D, 

            -A3D6D, -C1A, -C1B, -C1C, -C1C6, 

            -C1D6, -C1E6, -C1E6D,  -C1F, 

            -C1G6,  -D1A, -J1AD, -J1A6D, -K2A 

LIO-360-C1E6 

AIO-360-A1A, -A2A, -A1B, -B1B 

AEIO-360-A1A, -A1B, -A1B6, -A1C, -A1E, 

              -A1E6, -A1D, -A2A, -A2B, -A2C 

IO-360-B1A, -B1B, -B1D, -B1E, 

    -B1F, -B1F6, -B2E, -B2F, 

    -B2F6, -B1G6, -B4A, -E1A, -F1A, 

-M1A+ 

AEIO-360-B1B, -B1D, -B1F, 

     -B2F, -B4A, -B1F6, -B2F6, 

     -B1G6, 

Oil, Lubrication 

(Lubricants should conform to the 

specification as listed or to 

subsequent revisions thereto) Lycoming Spec. No. 301 and Service 

Instruction 1014 - - 

Temperature NOTE 1 - - 

Pressure NOTE 2 - - 

Sump capacity, qt. 8 - - 

(Except AIO series) AIO series - Dry Sump ? 

Usable oil qt, (Except AEIO series) 6 - - 

Engine Position NOTE 14 - - 

Usable oil qt., (AEIO series) 4 - - 

Ignition, dual 

Magnetos NOTE 7 - - 

Timing °BTC 25* 25 

Spark plugs NOTE 4 - - 

Bore and stroke, in. 5.125 x 4.375 - - 

Displacement, cu. in. 361 - - 

Compression Ratio 8.7:1 8.5:1 

Turbocharger NOTE 9 - - 

Weight (dry) lb. NOTE 7 - - 

C.G. Location (dry with starter 

   and generator installed) NOTE 7 - - 

Propeller shaft, SAE No. AS-127 Flange, Type 2 Modified - - 

Crankshaft Dampers and Balancers NOTE 12 - - 

NOTES 1,2,3,4,5,7,8,9,10,11,12,16 1,2,3,4,5,7,10,11,12,16 

"- -" indicates "same as preceding models" 

"?" indicates "does not apply" 

+ IO-360-M1A has an alternate rating of 160 BHP at 2400RPM 

*  All models except IO-360-A1B6D and -A3B6D have optional timing of 20°BTC

 

[Ned Gravel]

I have been told mine are set at 20 BTDC.  I asked about the effect of changing them to 25 BTDC based on the discussion on Mooneyspace.  No answer yet.

 

[Shadrach]

25 BTDC.  My engine runs beautifully LOP or ROP. It also outclimbs and outcruises most of it's siblings judging from what others have said.  I see no utility in the retarded ignition other than slightly cooler take off CHTs...

[jetdriven]

If you can keep your CHT in line, 25 degrees is the way to go.  Lower fuel flow on the same speed, or the same fuel flow with a 2-5 knots more. ESPECIALLY LOP or at high altitude. Only one way to get that, plain more efficiency.

 

Ross your F is one of the best years, 1967.   And a fast one too . You would be right beside our J which is ten years newer, likely a couple knots faster..  With more useful load than us.

[garytex]

Thanks for the answers.  I'll have my mechanic set mine at 25 BTDC if it isn't already.  (I am still scared of the buzzer and flashing lights)

Sincerely,

Gary

[1964-M20E]

I'll throw in my $0.02 from my general knowledge of engines and that is

 

@ 25 BTC

Pros

you will get more performance from the engine

while required for airworthiness, 25 BTC makes 100LL much more of a necessity

Cons

the engine is more susceptible to pre-ignition

 

@ 20 BTC

pros

the engine is less susceptible to pre-ignition, the engine can tolerate lower octane fuel better

cons

you will get less performance

 

So if you manage you engine correctly 25 BTC is the way to go, if not, you may find yourself feeding it pistons and cylinder heads.

[jetdriven]

The only downside is we have noticed a higher CHT during OATs over 80 degrees. Instead of an easy "no worry"  360 on the hottest two, its more like an easy 380, you can aggressively lean too much in climb and hit 400.  Lenaing in cruise, we just go 15 LOP and watch it. So far, 375 is normal.  360 is attainable. Leaningn a little more nets the same speed and timing as with 20 degrees, but a little less fuel flow.  We cna also lean to 5.0 GPH during procedure turns and holds, around 105 KIAS. 

Today we flew 26.5-27", 2500 RPM, 3500 feet MSL,  LOP FF was 9.3 GH and the hottest cylinder (#4) was 310.  Around 145 KIAS.

 

100LL is the only option.   There is precious little MOGAS available anymore.

[garytex]

Thank you for the input.  

I have been waiting with baited breath to get my hands on my just purchased F model.  It is at Dugosh getting a new oil cooler, the $300 square accordion intake fitting, and a flap jack shaft bell-crank attach point crack fixed.  (if you got the flap jack shaft, does that mean the lady at IHOP brought you no pancakes?)  I'll have them check the timing (I'm still afraid of the buzzer and flashing lights) and hopefully not forget to unfold the feet after I'm done with my complex checkout.  

This is a great forum and a wonderful information source, a reflection of the members.

Thanks again,

Gary 

[takair]

There was a Lycoming Service Instruction put out some years ago that apparently changed timing on the IO-360's due to high CHT and low detonation margins in cold weather (it's coming).  It was SI-1325a.  I can't put my hands on it now.  I know my IO-360A1A had it's data plate changed to reflect 20 degree timing from the original 25.  The official timing of your particular engine should be on the data plate. Will try to get ahold of SI-1325a to see what it says.

[N601RX]

I'm not sure if SI 1325a is on lycomings webpage or not, but if  not I have a copy if anyone needs it.  It also involves changing the impulse couplings on certain engines in addition to setting the timing back to 20 deg as well as replacing the engine name plate.

[takair]

For some reason it is not on the web page.  Do you have an electronic copy?  I can PM my email.

Thanks

Quote: N601RX

I'm not sure if SI 1325a is on lycomings webpage or not, but if  not I have a copy if anyone needs it.  It also involves changing the impulse couplings on certain engines in addition to setting the timing back to 20 deg as well as replacing the engine name plate.

[tony]

I did a prety good google search and I can't find it.  I assume if the SI was performed in the past, it would be reflected with a new data plate on the engine? Now you guys are going to make me go look at the data plate the next time I'm out at the hanger.

[N601RX]

Quote: takair

 

[Shadrach]

Quote: jetdriven

The only downside is we have noticed a higher CHT during OATs over 80 degrees. Instead of an easy "no worry"  360 on the hottest two, its more like an easy 380, you can aggressively lean too much in climb and hit 400.  Lenaing in cruise, we just go 15 LOP and watch it. So far, 375 is normal.  360 is attainable. Leaningn a little more nets the same speed and timing as with 20 degrees, but a little less fuel flow.  We cna also lean to 5.0 GPH during procedure turns and holds, around 105 KIAS. 

Today we flew 26.5-27", 2500 RPM, 3500 feet MSL,  LOP FF was 9.3 GH and the hottest cylinder (#4) was 310.  Around 145 KIAS.

 

100LL is the only option.   There is precious little MOGAS available anymore.

[jetdriven]

Interesting. I cannot find SI-1325A anywhere.  Also, is a SI regulatory?

 

[Immelman]

Next time you guys have your right side cowl off look at the data plate on your engine. It will list the spark advance.

On the IO-360-A1A in my airplane, the data plate says 20 degrees BTDC.... then I look at the ring gear on my engine, and its timing mark is at 25 degrees! My A&P/IA believes the correct thing to do is to follow the data plate in this case.

I am not an A&P/IA but I would be hard pressed to believe that advancing the timing (on my particular engine, with that data plate) is kosher (though I would prefer the slight performance boost, no doubt!), so before you guys get out your protractors and buzz-boxes have a look at the data plate.

 

[N601RX]

Quote: Immelman

Next time you guys have your right side cowl off look at the data plate on your engine. It will list the spark advance.

On the IO-360-A1A in my airplane, the data plate says 20 degrees BTDC.... then I look at the ring gear on my engine, and its timing mark is at 25 degrees! My A&P/IA believes the correct thing to do is to follow the data plate in this case.

I am not an A&P/IA but I would be hard pressed to believe that advancing the timing (on my particular engine, with that data plate) is kosher (though I would prefer the slight performance boost, no doubt!), so before you guys get out your protractors and buzz-boxes have a look at the data plate.

 

[N601RX]

Service Instruction No. 1325A
(Supersedes Service Instruction No. 1325)
Engineering Aspects are
FAA (DEER) Approved
DATE: May 14, 1976
SUBJECT:
MODELS AFFECTED:
TIME OF COMPLIANCE:
Timing Change for IO-360 Series Engines
IO-360-A series (not -A1B6D), -C, -D series, HIO-360-C1A, -C1B, AEIO-
360-A1B6 with serial numbers prior to 14435-51; IO-360-C1D6 with
serial numbers prior to 14445-51, LIO-360-C1E6 with serial numbers
prior to 1063-67 and AIO-360-A1A, -A1B, -B1B with serial numbers prior
to 219-63; TIO-360-A1B with serial numbers prior to 145-64. See
Service Bulletin No. 380 for IO-360-C1C and -C1F models.
At overhaul or at owner's discretion.
Certain advantages in engine operation have
been found by changing engine timing from 25°
BTC to 20 BTC and reducing the lag angle to
15° on impulse coupling magnetos and 15
retard angle on retard breaker magnetos whi-chever
is applicable. Significant improve-ments
in engine operating characteristics are
achieved in above listed aircraft engine
installations particularly in the areas of
normal operation and cold weather starting.
During cruise operation, cooler cylinder head
temperatures can be expected resulting in
improved service life of intake and exhaust
valves. During full throttle operation the
new spark setting will reduce possibility of
detonation during extreme cold weather opera-tion.
Consequently this modification has been
incorporated in the production of new engines
and may be incorporated in engines in service
as follows:
1. Remove the left magneto and determine if
it has an impulse coupling or if it is a
retard breaker magneto; if it is a retard
breaker magneto it cannot be converted to
the 15 retard angle. However, a Bendix
blue magneto which incorporates a 15 re-tard
angle is available through Avco Ly-coming
distributors. See "Parts Data" be-low.
Install the replacement magneto as
described in step 3.
2. If the left magneto has an impulse
coupling, replace the coupling with a new
one, LW-391429 on all models except reverse
rotation engines; on these use impulse
coupling LW-391427.
3. Install the magneto on the engine and
retime both magnetos using the 20 timing
mark on the starter ring gear instead of
the 25 mark. See Avco Lycoming Operator's
Manual 60297-12 for ignition timing proce-dure.
4. Replace the engine nameplate with a new
one, Avco Lycoming P/N 61548 which indi-cates
new timing angle. Also restamp the
magneto nameplate to indicate the magneto
is -9, -10 or -55 instead of -3, -6 or -45.
PARTS DATA:
15 Lag Angle
Magneto
LW-349365-9
LW-349365-10
LW-51360-55
Replaces
Magneto
LW-349365-3
Magneto
Model Engine Application
S4LN-1227 IO-360-A1B,-A1B6,-C1C,-C1F,-C1D 6, -C1E6, AIO-360-A1A,
-A1B, -B1B, AEIO-360-A1B6
LW-349365-6 S4RN-1227 LIO-360-C1E6
LW-51360-45 S4LN-21 IO-360-A1D

PARTS DATA (CONT.):
15° Retard Angle
Magneto
LW-349285-7
LW-349285-8
LW-163005-11
LW-163005-12
Replaces
Magneto
LW-349285-1
LW-163005-2
Magneto
Model
S4LN-1208
S4RN-1208
S4LN-200
S4RN-200
Engine Application
IO-360-A1C, -C1C, -D1A; HIO-360-C1B; AIO-360-
A1A; TIO-360-A1B
LHIO-360 C1B
IO-360-AlA, -A2A, -C1A; HIO-360-ClA; AEIO-360-
A1A
LHIO-360-C1A
LW-391429
LW-391427
61548
18484, 18485 -
Impulse coupling, 15° lag angle (replaces LW-349359)
Impulse coupling, 15 lag angle (replaces LW-349358 for magnetos on reverse ro-tation
engines)
Engine nameplate (replaces nameplate with 25° BTC timing specified). See Ser-vice
Instruction No. 1304 for procurement procedure.
These numbers for Avco Lycoming reference only.

[takair]

Quote: jetdriven

Interesting. I cannot find SI-1325A anywhere.  Also, is a SI regulatory?

 

[jetdriven]

How about our data plate, with a poorly (and undocumented) 0 stamped over the 5 in the "25".   Although the SI and the TC both say 20 is optional except -A3B6D.     

[takair]

Quote: jetdriven

How about our data plate, with a poorly (and undocumented) 0 stamped over the 5 in the "25".   Although the SI and the TC both say 20 is optional except -A3B6D.     

[jetdriven]

About 5-7 knots TAS when LOP.  Around the same in a full bore air race.   The "D" engine has a single mag, so no provision for retarded impulse couplings.  It actually starts easier at 25. 

 

20 degrees is more conservative if you count cylinder pressure on takeoff.  Im not sure how that correlates to cracks or wear. The enigne is certified to produce 200 HP continuous, and back-timing it to effectively de-rate it sounds ridiculous.    It is less conservative, and perhaps more dangerous, when you need climb capability for a short field takeoff. Especially on a high density alritude day.   Our climb rate has improved by quite a bit, perhaps 10-15%. If the engine fails on takeoff, a higher altitude gives you more margins.

[kellym]

Quote: jetdriven

About 5-7 knots TAS when LOP.  Around the same in a full bore air race.   The "D" engine has a single mag, so no provision for retarded impulse couplings.  It actually starts easier at 25. 

 

20 degrees is more conservative if you count cylinder pressure on takeoff.  Im not sure how that correlates to cracks or wear. The enigne is certified to produce 200 HP continuous, and back-timing it to effectively de-rate it sounds ridiculous.    It is less conservative, and perhaps more dangerous, when you need climb capability for a short field takeoff. Especially on a high density alritude day.   Our climb rate has improved by quite a bit, perhaps 10-15%. If the engine fails on takeoff, a higher altitude gives you more margins.

[Shadrach]

Quote: kellym

I was pointed to this dicussion by someone confused by the discussion. You need to keep several things in mind. An A&P must set your timing to the specs on the engine data plate. That is the only place he can legally set it.

Changing the timing from 25 to 20 or 25 to 20 changes the timing during starting as well. For best starting you need the engine firing at TDC, not 5 degrees before or after TDC.

If your engine was overhauled, rebuilt or manufactured by Lycoming after the SI1325 came out, it WILL have 20 degree timing. You can't legally change that without getting blessing to change your engine data plate.  If your engine last saw Lycoming before 1976, it will have 25 degree timing. You can choose to do the Service Instruction, or you can ignore it. It is not something you should contemplate going back and forth, as the mags do have to have internal parts changed to have the timing during cranking correct.

If you advance the timing on a 20 degree engine to 25, your engine will attempt to start at 5 degrees before TDC. Depending on cranking speed you are at risk of a kickback, which will destroy some starters.

 

[jetdriven]

Kelly: Can you look at the following pages 1 and 2 from the 1E10 TCDS and tell me what timing my IO-360-A3B6D should have?